PLANT SECONDARY METABOLITE DIVERSITY AS A RESISTANCE TRAIT AGAINST INSECTS - A TEST WITH SITOPHILUS-GRANARIUS (COLEOPTERA, CURCULIONIDAE) AND SEED SECONDARY METABOLITES

A hypothesis is tested about the functioning of plant secondary metabo lite diversity taking into account the role of concentration of mixtur es or single compounds: a high diversity secondary metabolite mixture in high concentration provides a more effective protection against her bivores than single compounds or low diversity mixtures in both low an d high concentrations. Additionally the role of two unusual secondary metabolites for a weevil when they are incorporated in its diet is exp lored. Number of eggs laid and diet consumption are measured in the gr anary weevil Sitophilus granarius exposed to cereal and non-cereal sec ondary metabolites incorporated in artificial diets to test the hypoth esis. Artificial diets had one, two, four or six compounds. The mixtur es or single compounds were offered simultaneously to the weevils in c oncentrations ranging from 0.05 to 5mgg(-1) in a multiple choice exper iment. Low oviposition in high concentration six compounds mixture sup ported the hypothesis. However, low oviposition in a low concentration mixture of four compounds suggests that a moderate diversity may be e qually functional in low and high concentrations. Diet consumption by the weevil was not affected by concentration but an increasing number of compounds in the diet reduced it slightly but significantly. The un usual secondary metabolites for the weevil were less or equally effect ive reducing oviposition and consumption as usual compounds did. (C) 1 997 Elsevier Science Ltd.